This invention relates to hydraulic or fluid couplings and, more particularly, to a hydraulic or fluid coupling having an input member characterized as a bladed primary wheel, and an output member, characterized as a bladed secondary wheel, confining an operating space.
A hydraulic coupling transfers energy from a drive motor to a production machine. In the case of a production machine having a large load or mass or which conveys large loads or masses, e.g. conveyor belts, the hydraulic coupling ensures that the drive motor starts up at a low load. Once the drive motor has attained its rated speed, the production machine is set in motion. During the start-up phase of the production machine, the hydraulic coupling automatically limits the transmitted torque to a specific desired value, thus reducing stress on both the drive motor and the production machine.
The invention relates exclusively to hydraulic couplings constructed such that they can be operated by a constant quantity of fluid, i.e. with the coupling at rest, its inner chamber is filled by a definite volume of working or operating fluid and the volume remains unchanged during operation. Hydraulic couplings having at least one delay chamber rotating with the primary blade wheel in which part of the operating fluid accumulates when the coupling is at rest, are known. This construction permits the possible reduction in the torque transmitted by the coupling during the start-up phase and maintains coupling torques during start-up within certain limits. Other types of hydraulic couplings have an external influence on the fluid level in the operating space, e.g. by means of a scoop tube. These type of couplings may have similar properties. However, the additional expense for the external influence is only worthwhile in the case of high power levels.
A hydraulic coupling is disclosed in German Auslegeschrift No. 12 02 592 which has two delay chambers arranged at the rear side of two blade wheels for the purpose of attaining coupling symmetry. The two delay chambers are located relatively close to the coupling axis of rotation. At approximately the radial center of the operating space, the two blade wheels are provided with overflow channels connecting the delay chambers to the operating space. One of the two delay chambers is also connected to the operating space by way of the outer annular gap existing between the blade wheels.
Further, in German Pat. No. 3231368 and U.S. Pat. No. 4,516,399 there are disclosed hydraulic couplings with only a single delay chamber. In accordance with the disclosure of these patents, the greater the volumetric capacity of the delay chamber, the greater is the possible reduction in the torque transmittal by the hydraulic coupling during the start-up phase. Thus, it is suggested that it is possible to maintain relatively low coupling torques during start-up within certain limits by increasing the size of the delay chamber. In addition, applying further measures as described in DE No. 3231368, the coupling torque, after an initial steep parabolic rise to approximately one-half of its maximum value, can be made to rise to its maximum value at a slow rate. Thus, an advantage is achieved by attaining a relatively delayed maximum coupling torque.
The measures disclosed in the above-noted patents were steps in the right direction. However, in the case of production machines with particularly heavy start-up loads, e.g. conveyor belts, the development of coupling torques during start-up are stil too rapid and the shock load occurring during the start-up will reduce the operating life of the conveyor belt.